Single and multiple (e.g. twin) screw feeder apparatus is known, whereby a composition of an organic polymer can be delivered to a die or mould assembly for extrusion or moulding. The screw or screws are housed in a barrel and rotate so that the screw flights carry the composition along the barrel. It is also known that the root diameter of the shaft of such screws can vary along the length of the screw, so that the composition can be subjected, during its journey along the barrel, to varying degrees of compression and heating, which are necessary to prepare the material for extrusion or moulding.
Some organic polymers are more susceptible than others to damage from such compression, especially if they are excessively chopped and broken up. For example, certain grades of polyvinyl alcohol can degrade, leading to a cloudy, hard product where a clear flexible film might have been intended. This degradation has been attributed to cross-linking. It would therefore be desirable to pass such material through such heating and working zones as are necessary but without breaking it up.
Multilayered co-extruded films can be made by providing a plurality of such apparatuses in parallel, with means for uniting the parallel newly extruded films, which would typically have different but carefully coordinated properties, as described in for example International Application PCT/WO93/22125.